Avoid passing NULL to the xOpen method of an FTS3/4 tokenizer.

FossilOrigin-Name: 0dd09fc034c127718366d3a3183e367d2f9fd82d

test/fts3atoken.test

@@ -24,6 +24,8 @@ ifcapable !fts3 {
   return
 }
 
+set ::testprefix fts3token
+
 proc escape_string {str} {
   set out ""
   foreach char [split $str ""] {
@@ -167,8 +169,18 @@ ifcapable icu {
   do_icu_test fts3token-4.8 en_US  $input $output
 }
 
+do_execsql_test 5.1 {
+  CREATE VIRTUAL TABLE x1 USING fts3(name,TOKENIZE icu en_US);
+  insert into x1 (name) values (NULL);
+  insert into x1 (name) values (NULL);
+  delete from x1;
+}
+
 do_test fts3token-internal {
   execsql { SELECT fts3_tokenizer_internal_test() }
 } {ok}
 
+
 finish_test
+
+